1. Field of the Invention
The present invention relates to weighing devices and, more particularly, to a piezoelectric device that determines the actual weight of a given sample.
2. Brief Description of the Prior Art
Applicant's Assignee is in the business of determining the amount of carbon residue in petroleum-based materials. During processing of petroleum products, engineers want to know as expeditiously as possible the amount of high-boiling components in the petroleum products being processed. The lighter carbon products (such as gasoline, kerosene, and oil) have very small amounts of carbon residue. These products, which are sometimes referred to as "light" petroleum products, will quickly boil off if the temperature of the substance being processed is raised to approximately 500.degree. C. However, the heavier petroleum products having larger, more complicated molecules would remain. This material is often referred to as carbon residue and may resemble tar. If the amount of carbon residue during the manufacturing process is too great, the manufacturer has one of two alternatives; namely, either use the carbon residue for low-profit items, such as the making of asphalt, or further processing the carbon residue in an attempt to "crack" the carbon residue molecules into lighter products. Sometimes the cracking is very expensive and costly. The processor of petroleum products wants to know as expeditiously as possible the amount of carbon residue that is in the petroleum product being processed so that the processor can make a decision on what additional processing steps, if any, need to be taken.
In the past, it has required a considerable length of time and laboratory work to determine the amount of carbon residue in a petroleum-base product. The most common method used in determining carbon residue was referred to as the Conradson Carbon Residue Test. This entailed the weighing of a sample, heating the sample until the light particles evaporate, and subsequently measuring the weight of the residue. This would give both weights from which a percent of carbon residue could be determined. These methods used in the Conradson Carbon Residue Test would normally take a couple of hours of laboratory time and would not give any type of instantaneous result so that the manufacturing process of petroleum-based products could be rapidly changed.
Various types of alternatives to the Conradson Carbon Residue Test have been developed, such as those described in an article by F. Noel entitled "An Alternative to the Conradson Carbon Residue Test", which is incorporated herein by reference. Mr. Noel uses a carbon residue test which uses extremely small samples to determine the amount of carbon residue. The present invention is an apparatus that can be used in measuring the extremely small sample sizes suggested by Mr. Noel.
In the field of weights and measures, it is extremely difficult to accurately weigh a small sample size. Dust, vibrations, wind, humidity or breath of the person making the measurements could affect the weight measurement. The parent application was directed towards the use of vibrating piezoelectric devices that may give a ratio of weights, but never actually know the quantity of the weights being measured. The present application is directed towards use of the same device to determine absolute weights, which is easily accomplished through calibration techniques. The piezoelectric device may have a driver element and, by measurements being taken from a receiver element, a signal proportional to the weight of the substance being measured is obtained.
In the past, piezoelectric ceramics have been commonly used in the industry to create resonant frequencies. The piezoelectric ceramic may act as either a receiver or driver. A good descriptive article entitled "Piezoelectric Ceramics" by Eric A. Kolm, et al. published in Mechanical Engineering, February 1984, p. 43, explains the operation of piezoelectric devices.
Many different types of weighing devices have been designed in the past that will eliminate vibrations and weigh small amounts, such as those shown in U.S. Pat. No. 4,088,014 to Wirth; U.S. Pat. No. 3,967,497 to Brown; U.S. Pat. No. 1,974,940 to Wood; U.S. Pat. No. 3,133,606 to Thomson; U.S. Pat. No. 3,680,650 to Zimmerer; U.S. Pat. No. 994,733 to Feinstein; and U.S. Pat. No. 633,471 to McGarvey. Other types of vibrating string weighing devices are shown in the prior art, such as illustrated by U.S. Pat. No. 3,701,392 to Wirth. However, Wirth simply stresses the vibrating mechanism itself. Another type of vibrating string mechanism that uses magnets is shown in U.S. Pat. No. 4,383,585 to Gauss.
However, none of the patents referred to hereinabove in any way suggest a piezoelectric type of device being used to determine the absolute weight of a small sample size using a system wherein the piezoelectric crystal is the driver and the receiver. Further, none of the prior art discloses any type of on-line system for a petrochemical processing plant whereby the amount of carbon residue can be monitored on an essentially continuous basis during the manufacturing process. An on-line device for determining carbon residue must be suitable for operation in the adverse environment of a petrochemical plant without requiring an undue amount of special consideration.